Development and experimental study of steel beam-through framed connections with T-type curved knee braces for improving seismic performance

Abstract

This paper introduces beam-through framed connections (BTFCs) with innovative T-type curved knee braces (TCKBs). Beam-through steel frame (BTF) is an emerging system using strip braces as lateral force-resisting components. Even though strip braces can provide high strength and stiffness, they will get slack after yielding since compressive buckling, and dynamic characteristics of the system will be unstable. Innovative T-type curved knee braces are intended to provide stable strength and full energy dissipating capacity. By equipping a BTF with TCKBs, seismic performance of the system can be improved, and architectural space can be released. In order to verify the reasonability of construction details, investigate failure modes and damage sequences, a total of three full-scale specimens with different TCKBs were designed and tested under incremental cyclic loading. Results of tests demonstrated the expected stable hysteretic behaviors, controllable damage sequences and superior ductility. Damages were mainly concentrated on knee braces within 2.0% drift ratio. With subsequent increase of the loading amplitude, plasticity was observed on beam-to-column connection area. Tested knee braces started to be fractured when drift ratio reached 7.0% approximately which was treated as the failure mode. In the final stage of loading, webs of knee braces fractured one after another. After web of four knee braces fractured, specimen could still exhibit partial strength derived from damaged braces and semi-rigid beam-to-column connection which indicated the safety storage after failure mode.